feat(client): 标签打印预览弹窗（打印机选择 + 份数 + 所见即所得预览）

- 新增 LabelData 模型统一聚合单张标签字段（qrBytes/copies 等）
- 抽取 _renderLabelBitmap 共享位图绘制逻辑，TSPL 裸发与预览渲染完全一致
- 新增 renderLabelPreview / listLabelPrinters / detectDefaultPrinter 公开 API
- printProductLabel 新增 printerName 参数，透传到热敏裸发路径
- 新建 LabelPreviewDialog：缩略图条+大图主视图，打印机下拉+记忆（SharedPrefs）
  份数调整、勾选跳过、逐张打印进度状态显示
- 库存/商品详情/入库单 打标签 均接入预览弹窗，移除旧 _LabelPrintDialog

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

client/lib/screens/products/product_detail_screen.dart

@@ -8,6 +8,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter_riverpod/flutter_riverpod.dart';
 import '../../core/config/app_config.dart';
 import '../../core/utils/print_util.dart';
+import '../../widgets/label_preview_dialog.dart';
 import '../../core/theme/app_theme.dart';
 import '../../models/product.dart';
 import '../../models/product_image.dart';
@@ -656,8 +657,6 @@ class _QRCodeDialog extends ConsumerStatefulWidget {
 class _QRCodeDialogState extends ConsumerState<_QRCodeDialog> {
   late Future<Uint8List> _future;
   Uint8List? _bytes;
-  bool _printing = false;
-  String _printStatus = '';
 
   @override
   void initState() {
@@ -670,25 +669,25 @@ class _QRCodeDialogState extends ConsumerState<_QRCodeDialog> {
       });
   }
 
-  Future<void> _print() async {
-    if (_bytes == null || _printing) return;
-    setState(() { _printing = true; _printStatus = '正在打印...'; });
+  void _print() {
+    if (_bytes == null) return;
     final p = widget.product;
     final shopInfo = ref.read(shopInfoProvider).valueOrNull;
-    try {
-      await safePrint(context, () => printProductLabel(
-        qrBytes: _bytes!,
-        name: p.name,
-        code: p.code,
-        spec: p.spec,
-        series: p.series,
-        shopName: shopInfo?.name ?? '',
-        shopAddress: shopInfo?.address ?? '',
-        shopPhone: shopInfo?.phone ?? '',
-      ));
-    } finally {
-      if (mounted) setState(() { _printing = false; _printStatus = ''; });
-    }
+    final label = LabelData(
+      productId: p.id,
+      qrBytes: _bytes,
+      name: p.name,
+      code: p.code,
+      spec: p.spec,
+      series: p.series,
+      shopName: shopInfo?.name ?? '',
+      shopAddress: shopInfo?.address ?? '',
+      shopPhone: shopInfo?.phone ?? '',
+    );
+    showAppDialog(
+      context: context,
+      builder: (_) => LabelPreviewDialog(labels: [label]),
+    );
   }
 
   @override
@@ -717,15 +716,9 @@ class _QRCodeDialogState extends ConsumerState<_QRCodeDialog> {
           child: const Text('关闭'),
         ),
         FilledButton.icon(
-          onPressed: _bytes == null ? null : (_printing ? null : _print),
-          icon: _printing
-              ? const SizedBox(
-                  width: 14, height: 14,
-                  child: CircularProgressIndicator(strokeWidth: 2, color: Colors.white))
-              : const Icon(Icons.print, size: 16),
-          label: Text(_printing
-              ? (_printStatus.isNotEmpty ? _printStatus : '准备中...')
-              : '打印'),
+          onPressed: _bytes == null ? null : _print,
+          icon: const Icon(Icons.print, size: 16),
+          label: const Text('打印'),
         ),
       ],
     );